Method and device for the preparation of liquid samples in NMR spectroscopy using a combined titration and pH electrode

Abstract

A method and device have an electrode rod ( 1; 21 ) for a pH meter. The electrode rod ( 1; 21 ) has a measuring end ( 2; 22 ) for immersion into a liquid test sample ( 31 ), wherein the measuring end ( 2; 22 ) has a pH measuring element, and wherein electrical feed lines ( 5 ) in the electrode rod ( 1; 21 ) extend towards the pH measuring element. A plurality of capillaries ( 8, 9, 10; 23 ) for feeding liquids and gas into the test sample ( 31 ) extend in the electrode rod ( 1; 21 ) and have outlet openings ( 11, 12, 13; 24 ) in the area of the measuring end ( 2; 22 ). The method and device facilitate and accelerate preparation of liquid test samples and adjustment of a pH value for small amounts of test samples or narrow sample containers in NMR spectroscopy applications.

We claim: 
     
       1. A method for preparing a liquid sample for NMR spectroscopy using a combined titration and pH electrode having an electrode rod for a pH meter, the method comprising the steps of:
 a) positioning the electrode rod in a substantially vertical orientation with a measuring end thereof facing downwardly, the electrode rod measuring end being structured for immersion into the liquid sample, wherein the electrode rod comprises a pH measuring element disposed in the measuring end, electrical feed lines extending in the electrode rod to the pH measuring element, an acid capillary extending within the electrode rod for feeding an acidic fluid into the liquid sample, the acid capillary having an acid outlet opening in a bottom of the measuring end, a base capillary extending within the electrode rod for feeding a basic fluid into the liquid sample, the base capillary having a base outlet opening in the bottom of the measuring end, and a gas capillary extending within the electrode rod for feeding a gas into the liquid sample, the gas capillary having a gas outlet opening in the bottom of the measuring end; 
 b) immersing the measuring end into the liquid sample following step a); 
 c) discharging gas out of the gas opening following step b); 
 d) measuring a pH value of the liquid sample following or during step c); 
 e) if results of step d) indicate a measured pH value which exceeds a desired pH value, discharging acid out of the acid opening; 
 f) if results of step d) indicate a measured pH value which is less than a desired pH value, discharging base out of the base opening; 
 g) repeating steps c) through f) with the measuring end remaining immersed in the liquid sample until the measured pH value substantially equals the desired pH value. 
 
     
     
       2. The method of  claim 1 , wherein a buffer solution is supplied through a fourth capillary. 
     
     
       3. A device for preparing a liquid sample for NMR spectroscopy using a combined titration and pH electrode having an electrode rod for a pH meter, the device comprising:
 a mechanism for positioning the electrode rod in a substantially vertical orientation with a measuring end thereof facing downwardly, the electrode rod measuring end being structured for immersion into the liquid sample, wherein the electrode rod comprises a pH measuring element disposed in the measuring end, electrical feed lines extending in the electrode rod to the pH measuring element, an acid capillary extending within the electrode rod for feeding an acidic fluid into the liquid sample, the acid capillary having an acid outlet opening in a bottom of the measuring end, a base capillary extending within the electrode rod for feeding a basic fluid into the liquid sample, the base capillary having a base outlet opening in the bottom of the measuring end, and a gas capillary extending within the electrode rod for feeding a gas into the liquid sample, the gas capillary having a gas outlet opening in the bottom of the measuring end; 
 a mechanism for immersing the measuring end into the liquid sample; 
 a mechanism for discharging gas out of the gas opening; 
 a mechanism for measuring a pH value of the liquid sample; 
 a mechanism for discharging acid out of the acid opening if a measured pH value exceeds a desired pH value; 
 a mechanism for discharging base out of the base opening if the measured pH value is less than a desired pH value; and 
 a mechanism for cyclic adjustment of the pH value with the measuring end remaining immersed in the liquid sample until the measured pH value substantially equals the desired pH value. 
 
     
     
       4. The device of  claim 3 , wherein at least one of said acid, base and gas capillaries is made from glass, quartz glass of high purity, “fused silica”, metal, stainless steel, plastic material, PTFE (polytetrafuoroethylene), or PEEK (polyetheretherketone). 
     
     
       5. The device of  claim 3 , wherein said pH measuring element has a sensor chip or an ISFET (ion sensitive field effect transistor) and a reference electrode. 
     
     
       6. The device of  claim 3 , further comprising a temperature sensor disposed in an area of said measuring end. 
     
     
       7. The device of  claim 3 , wherein said electrode rod has an outer diameter of between 2 mm and 7 mm in an area of said measuring end. 
     
     
       8. The device of  claim 3 , wherein said capillary has an inner diameter of between 50 μm and 500 μm. 
     
     
       9. The device of  claim 3 , wherein said measuring end is pointed or beveled. 
     
     
       10. The device of  claim 3 , wherein said gas opening is closer to an end of said electrode rod than said pH measuring element. 
     
     
       11. The device of  claim 10 , wherein said acid and base openings are further away from an end of said electrode rod than said gas opening. 
     
     
       12. A titration unit having the device of  claim 3 , the titration unit comprising:
 a pH meter connected to said pH measuring unit; 
 an acid reservoir; 
 an acid pump connected to said acid reservoir to pass acid to one of said capillary outlet openings; 
 a base reservoir; 
 a base pump connected to said base reservoir to pass base to an other one of said capillary outlet openings; and 
 a mechanism for controlling said acid pump and said base pump to supply defined amounts of acid and base to the sample. 
 
     
     
       13. The titration unit of  claim 12 , wherein said controlling means is designed to automatically, iteratively adjust a pH value of the liquid test sample. 
     
     
       14. The titration unit of  claim 12 , further comprising a gas pump to supply gas through a capillary or through a lower capillary, wherein said controlling means drives said gas pump in such a manner that gas can be supplied during and/or after supplying acid and/or base. 
     
     
       15. The titration unit of  claim 12 , further comprising a buffer reservoir and a buffer pump for supplying buffer solution from said buffer reservoir through a capillary.